1. Field of the Invention
The present invention relates to a seal bar including a clamped seal element for rotary side seal machines and, more particularly, relates to a thin ribbon-like seal element constituted of a metallic high-temperature resistant material for the concurrent heat sealing and cutting through of superimposed layers of a thermoplastic film material.
The heat sealing and cutting through of superimposed layers of heat-sealable thermoplastic film materials, especially film materials for plastic bags which have side seals formed therein, as is well known in the plastic bag-making industry, frequently utilizes heat sealing arrangements incorporating elongated seal bars which are heated; for instance, through ultrasonic energy or an inductive electrical current. During operation of the arrangement, the seal bars are either reciprocated or rotated so as to contact the superimposed layers of the thermoplastic film material, to thereby fuse the layers together and thereby produce a heat seal between the film material layers, and to thereafter separate the heat-sealed layers through the intermediary of cutting blades or heated cutting elements which are interposed between spaced heated seal bars or located in close proximity thereto, so as to separate the heat-sealed film layers into separate segments.
2. Discussion of the Prior Art
Among various types of apparatus and methods which are known and employed in the technology for the formation of heat seals and the concommitant or closely following cutting through of the heat-sealed superimposed thermoplastic film material layers, especially for the side seals of plastic bags or the like, a considerable number of devices employ ultrasonics or an electrical current for either continuously or periodically heating a seal bar and/or heating a cutting element, the latter of which may be constituted of the so-called thin metallic ribbon-type cutter blades.
Fehr, et al. U.S. Pat. No. 3,574,039 discloses a film sealing and cutting apparatus wherein a transverse seal is formed to extend across the width of two superimposed thermoplastic film material layers through the physical application thereto of a pair of parallel spaced jaws each containing an electrically heated sealing bar which will fuse the film layers together, so as to produce a pair of closely spaced parallel heat seals. Thereafter, a heated cutting member in the shape of a thin blade which is interposed between the heated seal bars is advanced so as to cut through and separate the sealed film layers intermediate the parallel heat seals. This particular type of apparatus provides for the continuous heating of the sealing bars and the additional separate heating of the cutting member, while also imparting the sealing and cutting operation in two sequential operational steps, thereby rendering the entire apparatus and method highly energy-intensive and complex as being adapted primarily for use with intermittently advanced thermoplastic film web materials.
Rowley, et al. U.S. Pat. No. 3,640,790 describes an apparatus and method for the heat sealing and cutting through of superimposed layers of a heat-sealable thermoplastic film, in which a combined heat sealing bar and cutter fuses and melts the superimposed film layers through the application of pressure and heat thereto along the length of the sealing bar, thereby producing a heat seal between the layers while weakening the plastic material so as to facilitate the separation thereof along the seal while maintaining the facing and separated edges of the segments of the thermoplastic film in a sealed relationship with regard to the superimposed film layers.
Wheeler U.S. Pat. No. 3,687,789 relates to a heat sealing apparatus including a pair of closely spaced, parallel seal bars adapted to be heated so as to produce, upon contact, a pair of closely spaced longitudinal seals extending across superimposed layers of a heat-sealable thermoplastic film material, and with a heated metallic ribbon cutter being thereafter adapted to cut through the previously sealed film layers in the region of the seal so as to separate the film material into individual segments. This apparatus necessitates the ribbon cutting member be heated separately from and moved relative to the heated seal bars, rendering the entire apparatus and method of use thereof highly energy-intensive and relatively complex, while also being adapted primarily for the heat sealing of intermittently advanced webs of thermoplastic film material.
Schott, Jr. U.S. Pat. No. 3,775,225 discloses a machine for perforating and heat sealing a web of a multilayered thermoplastic film material for plastic bags, which incorporates a pair of heated elongate seal bars contacting the superimposed film layers to form two closely spaced parallel heat seals. Thereafter cutting of the sealed film layers is effected intermediate the formed heat seals through the advance of a heated cutting element between the seal bars, which may be a thin metallic ribbon-like cutting blade. This particular structure and method is also highly energy-intensive and complex, and is primarily designed for us with intermittently advanced webs of a thermoplastic film material.
Similarly, Kreager U.S. Pat. No. 4,517,790 provides for the formation of seals on packages or the like through reciprocating components in which an ultrasonic rotatable sealing bar or horn structure imparts a pair of parallel heat seals to superimposed layers of a thermoplastic film material, and with the film being cut into separate segments intermediate the formed seals through the action of a thin-bladed cutting element.
In order to improve upon the thermoplastic material heat sealing and cutting apparatus and methods of the prior art, somewhat more recently a heated seal bar structure has been developed for a rotary side seal plastic bag machine, wherein the heated seal bar is supported as a radial projection extending longitudinally along a rotating shaft or drum, and is fastened thereto by a series of post-like standoffs having ceramic insulating sleeves thereon. The seal bar, which is constituted of an electrically-conductive, high temperature resistant metallic material or alloy, such as nichrome or the like, comprises a generally thickly cross-sectioned electrically-heated resistance element which is generally heated to a temperature of approximately 1500.degree. F. through the constant application of an electrical current. During rotation of the shaft or drum, the seal bar element, which has a beveled taper along its outer edge to form a sealing and cutting edge, intersects an advancing layflat web of superimposed plastic film materials once for each revolution of the rotary shaft, so as to concurrently heat seal and cut through the superimposed film layers upon contact therewith.
Although this type of sealing bar device provides for a much simpler structure in comparison with those of the above-mentioned prior art patents, the elongate seal bar is subject to various limitations during the protracted use thereof. Thus, for instance, the mass of the thick elongate seal bar, which is only beveled toward its sealing and cutting edge, is high and necessitates the application of a constant electrical current to raise the seal bar to the necessary temperature in order to enable the sealing bar to carry out the desired heat sealing and cutting through of the film web layers, thereby resulting in a high electrical power consumption. Furthermore, the employ of a rather thick seal bar element which, when heated red-hot, for example, to a temperature of approximately 1500.degree. F. along its full length, produces a tendency in the bar to sag and warp between its supports, frequently causing difficulties to be encountered in the sealing bar heat sealing and cutting through the film web layers in an acceptable manner. Moreover, inasmuch as the currently employed sealing bar is constituted of rolled steel or similar material, and is imparted 45.degree. bevel or chamfer on each side of the sealing and cutting tip thereof so as to form a narrow sealing and cutting edge along its length, this necessitates precise beveling of the edge, and stoning thereof, rendering the cost of the equipment to be expensive. In addition thereto, in the event of a jam-up of the bag-forming machine, which is a frequently encountered phenomenon in actual practice, the thick or heavy sealing bar is frequently bent to such an extent as to be rendered unusable, and in the course of being bent may readily transmit damaging or even destructive stresses to its supports on the machine. Furthermore, replacing the heavy sealing bar element is, of necessity, a time-consuming procedure, which may increase the idle or downtime of the bag-forming machine, thereby considerably increasing operating and installation costs.